Polyolefins stabilized with mixtures comprising an acid phosphorus compound,a metal salt,and optionally a phenol



United States Patent ()fice 3,406,135 Patented Oct. 15, 1968 a a 18 Claims. (Cl. 260--23) ABSTRACT OF THE DISCLOSURE Stabilizer combinations are provided suitable for improving the resistance of olefin polymers to deterioration in physical properties on exposure to heat comprising an organic phosphorus acid containing trivalent phosphorus and a Group II metal salt of an organic acid, and optionally, a phenol and/or a triphosphite and/or a thiodipropionic acid ester. Olefin polymer compositions including such stabilizer combinations are also provided.

This application is a continuation-in-part of copending application Ser. No. 238,733, filed Nov. 19, 1962, now abandoned which is a continuation-in-part of Ser. No. 161,369, filed Dec. 22., 1961, now abandoned.

This invention relates to stabilizer combinations comprising an organic phosphorus acid and a polyvalent metal salt of an organic acid and optionally, other Olefin polymer stabilizers capable of improving the resistance of propylene polymer and other olefin polymers to thermal cracking when exposed to elevated temperatures and to olefin polymer compositions including such stabilizers and to propylene polymer compositions including such stabilizers.

Polypropylene is a tough, high-melting polymeric material, but in several respects its stability leaves much to be desired. The polymer shows a tendency to decrease rapidly in melt viscosity, and then to become brittle, when kept at elevated temperatures for the time required in milling, calendering, extrusion, injection molding and fiber-forming equipment. This deterioration is particularly serious when the polymer is worked in the molten state in the presence of oxygen, e.g., air. Shaped polymers prepared in such equipment show a tendency to discolor, to become distorted, to crack, and to powder around the edges upon exposure to sunlight and during aging, and especially when heated at moderately elevated temperatures, as in an accelerated aging process, and again, the problem is accentuated in the presence of oxygen. Polypropylene is particularly subject to deterioration in physical properties when exposed to high temperatures, of the order of 150 C. and above. It is now possible, using one or more stabilizers, to obtain a reasonably good stability against deterioration under most processing conditions except such high temperatures. Apparently, at such tempera- 0 tures the polypropylene undergoes thermal cracking, and many of the stabilizers which are effective to improve the stability under other processing conditions have a tendency to worsen the stability of the polypropylene against thermal cracking. Stabilizers which alone increase high temperature resistance tend to become ineffective in the presence of stabilizers added to correct other deteriorative tendencies.

For example, organic triesters of phosphorus acid at temperatures above 150 C. have a tendency to give black spots at high concentrations. Other stabilizers have a tendency to impart a distinct yellowing to the polymer during processing and heat aging at C. and above.

To meet commercial requirements, it is, of course, quite important that the polymer retain its physical properties during all temperature conditions that may be encountered during processing and thereafter. However, the art has experienced great difliculty in achieving the necessary heat stabilization.

Polypropylenes tend to differ in their deteriorative tendencies according to the process by which they are prepared. Apparently, molecular weight and stereo-regularity (tacticity) are factors. This complicates the development of a stabilizer which will make polypropylene sufficiently stable to be utilizable under high-temperature conditions. It would be an additional advantage if such a stabilizer could be incorporated either by the converter or by the manufacturer, without affecting or being itself affected disadvantageously by other stabilizer systems required to counteract other deteriorative effects.

In accordance with the instant invention, a stabilizer is provided comprising an organic phosphorus acid and a polyvalent metal salt of an organic acid, which in combination with other olefin polymer stabilizers or alone improves the resistance and/or resistance to embrittler ment of the olefin polymers, such as propylene polymers,

against thermal cracking, as evidenced by discoloration and/ or by an increase in melt index at elevated temperatures of 150 C. and above for long periods of time, and against discoloration upon aging as evidenced by the nitrogen dioxide test described hereinafter.

Purity of propylene polymers, extent of degradation, and resistance to embrittlement at elevated temperatures over long periods of time are characteristics capable of evaluation by observation of the change in melt index of the particular polymer when subjected to specified temperatures for a specified time. There is a direct correlation between the rate of increase in melt index and the rate of deterioration in the above-mentioned physical properties of the polymer.

Discoloration upon aging over long periods of time is a characteristic capable of evaluation by the nitrogen oxide test. Nitrogen dioxide (N0 is a gas produced in the burning of fuels and thus is found in the surrounding air as a pollutant. This gas is a powerful oxidizing agent and in the presence of water is acidic and thus, is quite similar to nitric acid. The effect which it has on a plastic such as polypropylene is indicative of the aging characteristics and the outdoor life of the plastic.

Combinations of organic phosphorus acid compounds and polyvalent metal salts of organic acids significantly reduce the rate of increase in melt index at elevated temperatures, improve resistance to discoloration upon exposure to nitrogen dioxide and also improve retention of color and other important physical properties of the propylene polymer.

For the purposes of this invention, the retention of physical properties at elevated temperatures is determined by tests carried out at 150 C., but it will be understood that the improvement is obtained at temperatures both above and below this temperature.

The organic phosphorus acids in accordance with the invention can be defined by the following formula:

In this formula, Z is an organic radical or radicals attached to the phosphorus through an oxygen or carbon atom. The Z radical can form a heterocyclic ring including the phosphorus atom in the ring, it can be two organic radicals attached to phosphorus through carbon or oxygen, and it can also include an addition OH group.

The organic phosphorus acids containing trivalent phosphorus of the stabilizer combination of the invention sti uc tlif e is s'till cont'foversial. Thus, 'the"stru cture may be written as formally trivalent phosphorus with an acidic hydroxyl, Z P- OH, or as formally pentavalent phosphorus with a P-'H bond,

and; e -z aa f c p osp o us a s-m y b tth lisht a 10 equation O POH [O] /P\ H For a -more detailed discussion of the structure and reactions of the organic phosphorus acids containing trivalent phosphorus of the stabilizer combination of the invention reference may-be made to the book Organophosphorus Compounds by G. M. Kosola-poff (John Wiley & Sons, N.Y. 1951), especially pages 144 and 193- 195.

Typical organic phosphorus acids which come within this general formula are the following:

II. (a)

. bivalent. torganicl valiphatic,

In theaboveformulae, R and R represent monovalent organic 'alipha'tic; aromatic and non aromatic alipyclic hydrocarbono'r heterocyclic radicals hav'in'gfi'om onegtovabbu't thirty carbon atoms, andR and R represent 7 aromatic or nonaromatic alicyclic hydrocarbon or 'heterocyclic radicals having from two to about thirty carbon atoms. R and R in Groups I and III may be the same or different.

The compounds of III are polymeric, n representing the number oierepeatingwunits enclosed by w-the brackets. 11 may have a value ranging from one to about thirty.

It will 'beceyident thatall vof these-compounds are organic-:phosphorus acid containing trivalent phosporus in which "there is at least one replaceable hydrogen per molecule and preferably one replaceable'hydrogen for each'phosphorus atom of the organic phosphorus acid. Thus, compounds of Groups I and II are prepared for use in the invention.

As exemplary of the compounds coming within Group I, there are suggested the following: di(phenyl) phosphite, monophenyl phosphite, mono-(diphenyl) phosphite, dicresylphosphite, di(o-is00ctylphenyl) phosphite, di(pethylhexylphenyl) phosphite, di(p-t-octylphenyl) phosphite, di(dimethylphenyl=) phosphite, di-n-butyl phosphite,

di-Z-ethylhexyl phosphite, mono-2-ethyl hexyl phosphite, diisooctyl phosphite, monoisooctyl phosphite, monododecyl phosphite, 2-ethylhexyl phenyl phosphite, 2-ethylheXyl-(n-octylphenyl) phosphite, monocyclohexyl phosphite, dicyclohexyl phosphite, di(2-cyclohexyl phenyl) phosphite, di-u-naphthylphosphite, diphenyl phenyl phosphite, di(diphenyl) phosphite, di-(2-phenyl ethyl) phosphite, dibenzyl phosphite, monobenzyl phosphite, nbutyl cresyl phosphite, didodecyl phosphite, ditetrahydrofurfuryl phosphite, difuryl phosphite, benzenephophonous acid, mono-Z-ethylhexyl benzenephosphonite, monophenyl butanephosphonite, -mono-2-butoxylethyl tat-naphthalenephosphonite, mono-n-octyl cyclohexanephosphonite, cctoluenephosphonous acid, diphenyl phosphinous acid, dibutyl phosphinous acid, benzyl methyl phosphinous acid.

Exemplary of compounds within Group II are: ethylene phosphite, propane-1-3-cyclic phosphite, 2-methylpropane- 1,3-cyclic phosphite, 2,2 dimethylpropane-l-,3 cyclic phosphite, 1,3-diphenylpropane-1,3-cyclic phosphite, butane-1,3-cyclic phosphite, 4-methylbutane-1,3-cyclic phosphite, SrmethyI butane-1,3-cyclic phosphite, 4-pheny1'butane-l,3-cyclic phosphite, 3-cyclohexylheptane-1,3-cyclic phosphite, l,3,7-triisopropylheptane-1,3-cyclic phosphite, and cyclohexane-1,3-cyclic phosphite.

Exemplary of organic phosphorus acid containing trivalent phosphorus coming within Groups 111a and I111:

are the compounds wherein R is neopentylene, ethylene, propylene-1,2, propylene-1,3, butylene-1,4, butylene-1,3, pentamethylene, hexamethylene, octamethylene, decamethylene, cyclohexylene, n-butylidene and diphenyl methane. In these compounds, R and R can be hydrogen, methyl, ethyl, propyl, butyl, isopropyl, isobutyl, isoamyl, phenyl, cyclohexyl and napththyl.

Exemplary of compounds coming within Group III!) are the compounds wherein R and R are any of those given abovein connection 111a and IIIb and R is any of the various radicals of the compounds of Group II. Exemplary of Group 111:: are:

Exemplary of Groups IIIc, d, e, and f are: HO -P l i OCBHH 0 1 CH3 I1 C and i: I u

O CgHn I The polyvalent metal organic acid salt will ordinarily have from about six to about twenty-four carbon atoms. The polyvalent metal can be any metal of Group II of the Periodic Table, such as zinc, calcium, cadmium, barium, magnesium and strontium. The alkali metal salts and heavy metal salts such as lead salts are unsatisfactory. The acid can be any organic non-nitrogenous monocarboxylic acid having from six to twenty-four carbon atoms. The aliphatic aromatic, alicyclic and oxygen-containing heterocyclic organic acids are operable as a class. By the term aliphatic acid is meant any open chain carboxylic acid, substituted, if desired, with nonreactive groups, such as halogen, sulfur and hydroxyl. By the term alicyclic it will be understood that there is intended and cyclic acid in which the ring is nonaromatic and composed solely of carbon atoms, and such acids may if desired have inert, nonreactive substituents such as halogen, hydroxyl, alkyl radicals, alkenyl radicals and other carbocyclic ring structures condensed therewith. The oxygen-containing heterocyclic compounds can be aromatic or nonaromatic and can include oxygen and carbon in the ring structure, suchas alkyl-substituted furoic acid. The aromatic acids likewise can have nonreactive ring substituents such as halogen, alkyl and alkenyl groups, and other saturated or aromatic rings condensed therewith.

,, As exemplary of the acids which can be used in the form of their metal salts there can be 'mentioned the following: hexoic acid, 2 ethylhexoic acid, n octoic acid, isooctoic acid, capric acid, undecylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, ricinoleic acid, behenic acid, chlorocaproic acid, hydroxy capric acid, benzoic acid, phenyl- I s H CH3 acetic acid, butyl benzoic acid, ethyl benzoic acid, propyl benzoic acid, hexyl benzoic acid, salicylic acid, naphthoic acid, 1 naphthalene acetic acid, orthobenzoyl benzoic acid, naphthenic acids derived from petroleum, abietic acid, dihydroabietic acid, hexahydrobenzoic acid, and methyl furoic acid.

The water-insoluble salts are preferred, because they are not leached out when the plastic is in contact with water. Where these salts are not known, they are made by the usual types of reaction, such as by mixing the acid, acid chloride or anhydride with the corresponding oxide or hydroxide of the metal in a liquid solvent, and heating, if necessary, until salt formation is complete.

The organic phosphorus acid-polyvalent metal salt combinations of the invention are effective stabilizers when used with olefin polymers, and especially propylene polymers, as the sole stabilizer. Their elfectiveness is particularly evidenced by an improved resistance to an increase in melt index upon exposure to elevated temperatures and an improved resistance to ageing as seen from the nitrogen dioxide test. They can also be used in conjunction with other olefin polymer stabilizers, wherein they are effective in overcoming disadvantageous effects contributed by the other stabilizers in the absence of the phosphorus acid. In many cases, an enhanced or synergistic effect is observed. Such additional stabilizers include, for instance, phenols, organic triphosphites, thiodipropionic acid esters, organic mercaptans, and organic polysulfides.

When the organic phosphorus acid-polyvalent metal salt stabilizer is used in conjunction with a phenol the increased stabilizing effect is evidenced by improved resistance to yellowing, and an extended life, in terms of resistance to embrittlement and development of tackiness at elevated temperatures. The phenol stabilizers contain one or more phenolic hydroxyl groups, and can contain one or more phenolic nuclei. In addition, the phenolic nucleus can contain an oxy or thio ether group.

The alkyl-substituted phenols and polynuclear phenols because of their molecular weight have a higher boiling point, and therefore are preferred because of their lower volatility. There can be one or a plurality of alkyl groups of one or more carbon atoms. The alkyl group or groups including any alkylene groups between phenol nuclei preferably aggregate at least four carbon atoms. The longer the alkyl or alkylenechain, the better the compatibility with polypropylene, inasmuch as the "phenolic Compound then acquires more of an aliphatic hydrocarbon character, and therefore there is no upper limit on the number of alkyl carbon atoms. Usually, from the standpoint of availability, the compound will not have more than about eighteen carbon atoms in an alkyl alicyclidene and alkylene group, and a total of not 'over about fifty carbon atoms; The compounds may have from one to four alkyl radicals per phenol nucleus.

The phenol contains at least one and preferably at least two phenolic hydroxyls, the two ormore hydroxyls being in the same ring, if there is only one, or in the same or different rings, if there are more than one. In-the case of bicyclic phenols, the'rings can be linked bythio" or oxyether groups, or by al-kylene,;'ali'cyclidene or arylidene groups. Such phenols, which are preferred because of their superior stabilizing action, can be defined by the formula: V r

(R1) n (R2) n,

where X is an oxygen or sulfur atom, or an alkylene or alicyclene or arylene or a mixed alkylene-alicyclene or alkylene-arylene or aryl-alkylene group, having a straight or branched chain, whose total number of carbon atoms ranges from one to about eighteen, y and y are the number of phenolic hydroxyl groups OH, n and :1 are the number of R groups, and R and R are hydrogen or alkyl of one to about eighteen carbon atoms. Preferably, the OH groups are ortho and/ or para to X.

The sum of y and n in each ring cannot, of course, exceed five.

The various X and R groups are exemplified in the following compounds.

Exemplary of satisfactory monohydric phenols are 2,6- di tertiary butyl 4 methyl phenol, 2 tertiary butyl- 4 methoxy phenol, nonyl phenol, dodecyl phenol, dinonyl phenol, phenyl phenol, tetradecyl phenol, and tetrahydro-a-naphthol.

Exemplary polyhydric phenols are orcinol, propyl gallate, catechol resorcinol, 4 octyl resorcinol, 4 dodecyl resorcinol, 4 octadecyl catechol, 4 isooctyl phloroglucinol, pyrogallol, hexahydroxy benzene, 4 isohexylcatechol, 2,6 di tertiarybutyl resorcinol, 2,6 diisoand propyl phloroglucinol, methylenebis(2,6 diterti arybutylm cresol), methylenebis (2,6 ditertiarybutyl phenol), 2,2 bis(4 hydroxy phenyl) propane, methylenebis(pcresol), 4,4 thio bis phenol, 4,4 oxobis(3 methyl- 6 isopropyl phenol), 4,4 thiobis(3 methyl 6- tertiarybutyl phenol), 2,2 oxobis(4 dodecyl phenol), 2,2 thiobis(4 methyl 6 tertiarybutyl phenol), 2,6 diisooctyl resorcinol, 4,4 n buty1idenebis(2- tertiarybutyL- 5 methyl phenol), 4,4 benzylidenebis (2 tertiarybutyl 5 methyl phenol), 2,2 methylenebis(4 methyl 6(1 methyl cyclohexyl) phenol), 4,4 cyclohexylidenebis(2 tertiarybutyl -,phenol), 2,6- bis(2' hydroxy -3 'tertiarybutyl 5' methylbenzyl)- 4, methylphenol, 4 octyl pyrogallol, and 3,5 ditertiarybutyl catechol.

When the organic phosphorus ac id -polyvalent metal salt stabilizer is'used in conjunction vvith triphosphite, the enhanced effect is evidenced in elimination of discoloration and fluxed for five minutes at :2 C. Pieces cut from concentrations, thus permitting use of larger amounts of triphosphite.

The triphosphite can be any organic triphosphite having attached to phosphorus throughoxygen or sulfur or a mixture of the same three groups each selected from aryl, alkyl, cycloalkyl, aralkyl and alkaryl groups in any combinations. Three monovalent groups (RA) P; one monovalent group, R; and one bivalent group, R forming a heterocyclic ring with the phosphorus,

a plurality of bivalent groups forming polymers therewith,

one trivalent group,

A Kil A and a plurality of trivalent groups R forming polymers therewith, I

A AH PARr PAR1 A AH and any combinations of monovalent, bivalent and trivalent groups to form monomeric and polymeric phosphites; wherein A is oxygen or sulfur. The term organic phosphite triester as used herein is inclusive of oxo, thio and mixed oxo thio phosphites. Usually, the phosphite will not have more than about sixty carbon atoms.

Exemplary are monophenyl di-Z-ethyl hexyl phosphite, diphenyl mono-Z-ethyl hexyl phosphite, di-isooctyl monotolyl phosphite, tri-Z-ethyl hexyl phosphite, phenyl dicyclohexyl phosphite, phenyldiethyl phosphite, triphenyl phosphite, tricresyl phosphite, tri(dimethylphenyl) phosphite, trioctadecyl phosphite, triistoctyl phosphite, tridodecyl phosphite, isooctyl diphenyl phosphite, diisooctyl phenyl phoshite, tri(t-octylphenyl) phosphite, tri(t-nonylphenyl) phosphite, benzyl methyl isopropyl phosphite, butyl dicresyl phosphite, isooctyl di(octylphenyl) phosphite, di(2- ethylhexyl) (isooctylphenyl) phosphite, tri(2-cyclohexylphenyl) phosphite, tri-a-naphthyl phosphite, tri(phenylphenyl) phosphite, tri(2-phenyl ethyl) phosphite, tridodecyl thio-phosphite, tri-p-tert-butyl phenyl thiophosphite, didecyl thiodiphenyl phosphite, tert-butyl phenyl thio-di- Z-ethylhexyl phosphite, ethylene phenyl phosphite, ethylene-tbutyl phosphite, ethylene isohexyl phosphite, ethylene isooctyl phosphite, ethylene cyclohexyl phosphite, 2- phenoxy-l,3-2-dioxaphosphorinane, 2-butoxy-1,3-2-dioxaphosphorinane, 2-0ctoxy-5,5 dimethyl-dioxaphosphorinane and 2-cyclohexyloxy-5,5-diethyl-dioxaphosphorinane.

When the organic phosphorus acid-polyvalent metal salt stabilizer combination is used in conjunction with a thiodipropionic acid ester, the improvement is evidenced by a materially prolonged resistance to embrittlement and development of tackiness at elevated temperatures. The thiodipropionic acid ester has the following formula: R OOCCH CH S-CH CH COOY in which R is an organic R radical selected from the group consisting of hydrocarbon radicals such as alkyl, alkenyl, aryl, cycloalkyl; mixed alkyl aryl, and mixed alkyl cycloalkyl radicals; hyd-roxy-alkyl and hydroxyalkyloxyalkylene radicals, and esters thereof with aliphatic carboxylic acids; and Y is selected from the group consisting of (a) hydrogen, (b) a second R radical R which can be the same as or different from the R radicals, (c) a polymeric chain of n thiodipropionic acid ester units (OOCCH CH SCH CH COOXO) giving a polymer having the formula:

-xoroccracn scrr cn cooxo OCCH2CH2-SCH2CH2COOZ where Z is hydrogen, R or M; n is the number of thiodipropionic acid ester units in the chain; and X is a bivalent hydrocarbon group of the type of R that is, alkylene, alkenylene, cycloalkylene, mixed alkylenearylone and mixed alkylene-cycloalkylene radicals; hydroxy alkylene and hydroxyalkyloxy alkylene radicals; esters thereof with aliphatic carboxylic acids; the value of n can range upwards from 0, but there is no upper limit on n except as is governed by the ratio of carbon atoms to sulfur atoms as stated below; and (d) a polyvalent metal M of Group II of the Periodic Table such as zinc, calcium, cadmium, barium, magnesium and strontium.

The molecular weights of the R and Y radicals are taken such that- With the remainder of the molecule the thiodipropionic ester has a total of from about ten to about sixty carbon atoms per sulfur atom.

Accordingly, the various thiodipropionic acid ester species coming within the above-designated categories within the general formula can be defined as follows:

(a) R OOCCH CH SCH CH COOH (b) R OOCCH CH SCH CH COOR (c) R OCCH CH SCH CH COOXO n1 OCCH CH SCHgCHgCOOZ (d) R OOCCH CH SCH CH COOM In the above formulae R and R M, X and Z are the same as before and the value of n can range upwards from 1, but there is no upper limit on n except as is imposed by the ratio of carbon atoms, as stated below. In the polymer (0), as in the other forms of thiodipropionic acid esters, the total number of carbon atoms per sulfur atom is within the range from about ten to about sixty.

The R radical of these esters is important in furnishing compatibility with the polypropylene. The Y radical is desirably a different radical, R or M or a polymer, where R is rather low in molecular weight, so as to compensate for'this in obtaining the optimum compatibility and nonvolatility. Where Y is a metal, the thiodipropionic acid ester furnishes the beneficial properties of the polyvalent metal salt which is described below.

The aryl, alkyl, alkenyl and cycloalkyl groups may, if desired, contain inert, nonreactive substituents such as halogen and other carbocyclic and heterocyclic ring structures, condensed therewith.

Typical R radicals are, for example, methyl, ethyl, proyl, isopropyl, butyl, isobu'tyl, t-butyl, amyl, isoamyl, n-octyl, isooctyl, 2-ethyl hexyl, t-octyl, decyl, dodecyl, octadecyl, allyl, hexenyl, linoleyl, ricinoleyl, oleyl, phenyl, xylyl, tolyl, ethylphenyl, naphthyl, cyclohexyl, benzyl, cyclopentyl, methylcyclohexyl, ethylcyclohexyl, and naphthenyl, hydroxyethyl, hydroxypropyl, glyceryl, sorbityl, pentaerythrityl, and polyoxyalkylene radicals such as those derived from diethylene glycol, triethylene glycol, polyoxypropylene glycol, polyoxyethylene glycol, 'and polyarylene radicals such as phenylene methylenephenylene dimethylene phenylene and alicyclene radicals such as cyclohexylene As exemplary of the thiodipropionic acid esters which can be used, there can be mentioned the following: monolauryl thiodipropionic acid, dilauryl thiodipropionate, butyl stearyl thiodipropionate, Z-ethylhexyl-thiodipropionate, diisodecyl-thiodipropionate, isodecyl phenyl thiodipropionate, benzyl lauryl thiodipropionate, benzyl phenyl thiodipropionate, the diester of mixed coconut fatty alcohols and thiodipropionic acid, the diester of mixed tallow fatty alcohols and thiodipropionic acid, the acid ester of mixed cottonseed oil fatty alcohols and thiodipropionic acid, the acid ester of mixed soybean oil fatty alcohols and thiodipropionic acid, cyclohexyl nonyl thiodipropionate, monooleyl thiodipropionic acid, hydroxyethyl lauryl thiodipropionate, monoglyceryl thiodipropionic acid, glyceryl monostearate, monothiodipropionate, sorbityl isodecyl thiodipropionate, the polyester of diethylene glycol and thiodipropionic acid, the polyester of triethylene glycol and thiodipropionic acid, the polyester of hexamethylene glycol and thiodipropionic acid, the polyester of pentaerythritol and thiodipropionic acid, the polyester of octamethylene glycol and thiodipropionic acid the polyester of p-dibenzyl alcohol and thiodipropionic acid, ethylbenzyl lauryl thiodipropionate, strontium stearyl thiodipropionate, magnesium oleyl thiodipropionate, calcium dodecylbenzyl thiodipropionate, and mono(dodecylbenzyl) thiodipropionic acid,

These esters are for the most part known compounds, but where they are not available, they are readily prepared by esterification of thiodipropionic acid and the corresponding alcohol.

The preferred stabilizer system of the invention comprises four stabilizers, the organic phosphorus acid, a polyvalent metal salt, a polyhydric phenol, and a thiodipropionic acid ester. An additional fifth ingredient which is included in the preferred systems of the invention, but which is not essential, is a triphosphite. These four and five stabilizers together give an enhanced stabilization which is not obtainable from any of them alone or in and cyclopentylene combinations of two or three. When taken alone, the components of this stabilizer system are capable only of inhibiting deterioration in one or two respects and quite large amounts may be needed before any effect is noted. The components other than the organic phosphorus acid and polyvalent metal salt may display a lesser stabilizing effect than any one alone. For example, the phenol alone gives an improved resistance to embrittlement and reduction in melt viscosity at elevated temperatures, but little assistance as to maintenance of color. The triphosphite alone is a rather poor stabilizer in preventing deterioration in the first two properties, but it does assist in resisting discoloration.

The thiodipropionic acid ester by itself only improves resistance to embrittlement. The polyvalent salt of an organic'acid by itself prevents discoloration, but no more. In combinations with the phenol, the color is worse than with the salt alone. i

In combinations with the triphosphite, the usual discoloration is prevented, but black spots may be obtained upon ageing at high triphosphite concentrations.

In view of this, it is surprising that the organic phosphorus acid, polyvalent metal salt, phenol, and thiodipropionic acid ester and optionally, triphosphite, taken together in 'the same total amount not only prevent discoloration but also embrittlement and inhibit the increase in melt index at processing temperatures with accompanying degradation of physical properties, and furthermore greatly enhance the resistance to discoloration and embrittlement on ageing to far beyond that obtainable from the components individually. This enhanced stabilizing effect is obtained with any propylene polymer regardless of the process by which it is prepared.

A very small amount of the organic phosphorus acidpolyvalent metal salt stabilizer combination is sufficient, with or without additional stabilizers, to improve the stability against deterioration in physical properties, including, for example, resistance to discoloration, under the conditions to which the olefin polymer will be subjected. Amounts within the range from about 0.005 to about 2.5% by Weight of the polymer impart satisfactory discoloration resistance at elevated temperatures. Preferably, from 0.01 to 1.0% is employed for optimum stabilization.

If additional stabilizers are employed to obtain additional stabilization effects, the amount of total stabilizer is within the range from about 0.005 to about preferably from 0.1 to 2.5%.

Preferably, the stabilizer system comprises from about 0.001 to about 0.25% of organic phosphor-us acid, from about 0.025 to about 0.75% of a polyvalent metal salt, from about 0.025 to about 0.5% of a phenol, andfrom about 0.05 to about 1% of a thiodipropionic acid ester, with optionally from about 0.025 to about 1.75% of an organic phosphite triester, when present.

If a combination of stabilizers is to be utilized, they may be formulated as a simple mixture for incorporation in the polymer by the polymer manufacturer or by the converter. An inert organic solvent can be used to facilitate handling, if the ingredients do not form a homogeneous mixture or solution.

The stabilizer of the invention is applicable to olefin polymers prepared by any of the various procedures, using the available catalyst, such as the Ziegler, ICI, Union Carbide, Du Pont, Phillips, Montecatini, Esso and Standard Oil (Indiana) process polymers, (Chem. & Eng. News, Nov. 21, 1960, pp. 36-59), for the molecular weight and tacticity are not factors affecting this stabilizer.

Formerly, olefin polymers prepared by these processes contained traces of catalyst residues. These residues materially diminished the stability of the olefin polymer, despite efforts to overcome the problem by addition of polyvinyl chloride resin stabilizers, Whose function was to act on the halogen or halide of the catalyst in the same manner as on the halogen or liberated halide of the polyvinyl chloride resin. It is now'customary to remove catalyst residues substantially completely, so that the addition of polyvinyl chloride resin stabilizers is no longer indicated. The stabilizers of the invention are effective with olefin polymers substantially free from catalyst residues, although they can also be used with catalyst-com taining polymers with good results. Isotactic polypropylene,- available commercially unde the tradenames Pro-Fax, Escon and Olefane and having a softening or hot-working temperature of about 350 F;, is an example of a sterically regular polypropylene polymer :1 v '2 Polypropylenesolid polymer can be defined in a mannet to differentiate it from other polyolefins as having a density within the range of from 0.86 to 0.91, and a melting point above C. The stabilizer of the invention is applicable to all such polypropylenes, as distinguished from polypropylenesin the liquid form or in semiliquid or gell-like forms, such as are'used as greases andwaxes. x 1 Mixtures of olefin polymers such as propylene polymers with other, compatible polymers and copolymers of propylene with copolymerizable monomers such as ethylene and butene also can be stabilized in accordance with this invention. For example, mixtures of polyethylene and polypropylene, and copolymers of propylene and ethylene which contain a sufiicient amount of'propylene to present the instability problem that is resolved by the stabilizer of the invention, can be stabilized by the addition of an organic'phosphorus acid alone or in combination with other propylene polymer stabilizers. The term propylene polymer as used herein includes, accordingly, homopolymers such as polypropylene, and propylene copolymers, and mixtures of propylene polymers, as discussed above.

The stabilizers of the invention can also be used with low density polyethylene, Ziegler polyethylene,high density polyethylene, poly(butene-l), poly (pentene-l), poly (3-methylbutene-1), poly-4-methyl-pentene-1, and polystyrene. The'term olefinpolyrner encompasses both homopolymers and copolymers, as well as mixtures of olefin polymers.

The stabilizer is incorporatedin the polymer in suitable mixing equipment, such as a mill ora Banbury mixer. If the propylene polymer has a melt viscosity which is too high forthe desired use, the propylene polymer can be worked until its melt viscosity has been reduced to the desired range before addition of the stabilizer. However, propylene polymers in a range of workable melt viscosities are now available. Mixing is continued until the mixture is substantially uniform. The resulting composition is then removed from the mixing equipment and .brought to the size and shape desired, for marketing or use. 7 p p The stabilized olefin polymer can be worked into the desired shape, such as by milling, calendering, extrusion or injection molding or fiber-forming. In such operations, it will be found to have a considerably improved resistance to reduction in melt viscosity during the heating, as well as a better re'sistanceto discoloration andembrittlement on ageing and heating.

The stabilizing effect of the organic phosphorus acid of the invention was evaluated in the working examples which follow using a modified ASTM D1238-57T test procedure for determining melt index, using a 2160 g. weight load on the plastometer piston, comparing melt index before and after heating the polymer in a mold at 600 F. for 30 minutes. The 600 F. temperature was selected as an extreme, resistance to which for the test period ensured stability to lower temperatures for considerably extended periods. The change in melt index for this period is an accurate measure of the degree of heat stabilization imparted by the stabilizeradded, irrespective of the numerical value of the initial melt indices of the dilferent samples of one particular polymer.

13 The lower the ratio the less the change, and the greater the stabilizing effect.

Example 1 In accordance with this invention diphenylphosphite and zinc 2-ethyl hexoate were weighed and dispersed by hand stirring in powdered previously unstabilized polypropylene (Profax 6501) in the proportions indicated in Table I, below. This polymer as supplied had-a melt index of 3.0, ASTM Dl238-57T at 230 C. The mixture 14 Example 3 Commercially available prestabilized polypropylene was compared with the same polymer to which diphenyl phosphite and/or zinc 2-ethylhexoate had been added as an additional stabilizer in accordance with this invention. A total of 0.05 to 0.1% stabilizer was used. The diphenyl phosphite and zinc 2-ethylhexoate were weighed and dispersed by hand stirring in powdered prestabilized polypropylene (Profax 6512 and Profax 6523). The mixture so prepared was in each case placed on a 2-roll mill and was placed on a 2-roll mill and fiuxed for five minutes fluxed for five minutes at l70i2 C. at 170:2" C. Pieces cut from the milled sheet were test- The stabilized polypropylene, sample B, was comed for heat stability in the above described manner.

TABLE III Parts Sample No.

EF GH.-I.J.K L

Polypropylene (Proiax 6512) 100 100 100 100 Polypropylene (Profax 5523) 100 100 100 100 Diphenyl phosphite 10 0.05 0.10 0.05 Zinc Z-ethylhexoate 0.05 0.10 0.10 0.05

pared with the unstabilized sample, A, of the same poly- The test results clearly indicated that the organic phosmer by testing pieces cut from a milled sheet of each phorus acid and zinc 2-ethylhexoate stabilizer combinasample composition in the above described manner. tion improved the resistance of these prestabilized poly- TABLE I propylenes to prolonged exposure at high temperatures, and that the effect of both was better than either alone. Sample NO. Parts The diphenyl phosphite and zinc 2-ethylhexoate limited A B the increase in melt index due to degradative deteriorapolypmpylene (Prom 6501) m0 100 tion on long-term exposure to elevated temperatures, and Diphenylphosphite 0.10 increased resistance to ageing at 150 C. In addition,

mate there was no noticeable discoloration. 1; 512 Example 4 fjfig iflggg1555: 355;555 Polypropylene alone and previously stabilized by ditertiary butyl p-cresol was further improved by the addifig g gfi lg figg gg 30 mm at F tion of 2,2-dirnethylpropane-1,3-cyclic phosphite and cad- 'Mm r/M,=Me1t Index Ratio indicating changeinmelt index. mium stearate. The stabilizers named in Table IV were The above data clearly indicate that the diphenyl phosg dispefsed by Fi stlmng m 100 parts of phite and zinc 2-ethyl hexoate increased the resistance of 223 F; i zg unstiblhzflfih.polyliropylene i g the polymer to degradative deterioration on prolonged exh d i i g f a gf as supli posure to elevated temperatures. The melt index ratio was 40 a met 5 f 2 T at 23(1) lower for the polymer containing the diphenyl phosphite n 9 i Part 0 y butyl p'creso was used, an additional 0.1 part of 2,2-d1-methyl-propane-1,3- and zinc Z-ethyl hexoate than for the polymer not stabilized in accordance with this invention. cyclic phosphite was added in two cases as indicated in Table IV. The mixture was in each case placed on a 2-roll Example 2 mill and fiuxed for five minutes at l70i2 C. Pieces cut Polypropylene stabilized by dilauryl thiodipropionate from the mlned Sheet were used In the testswas further improved by the addition of diphenyl phos- TABLE Iv phite and zinc 2-ethyl hexoate. The stabilizers named in Parts Table II were weighed and dispersed by hand stirring in Sample No. 100 parts of powdered previously unstabilized polypropyl- M N 0 P Q ene (Profax 6501). This polymer as supplied had a melt Polypropylene (Profax 6501) 100 100 100 100 100 index of 3.0, ASTM D1238-57T at 230 0. To each g gfggg gygtgggfgi gg- M5 polymer sample was added 0.50 part of dilauryl thiodiphosphite .1. 0.1 0.1 0.1 propionate by hand stirring; an additional 0.1 part of Cadmmm Stearate p y phosphite acid and P of Zinc zrethyl The results indicated that the addition of an organic Dale was added Sample as indicated in Table phosphorus acid and polyvalent metal salt in accordance Th6 mixture Was in ach Case Placed on 3 2411 mill with this invention increased the resistance of the polyn fi e for fi minutes at rL C- Pieces Cut f mer to degradative deterioration on prolonged exposure the milled sheet were used in the tests. to elevated temperatures. The addition of phosphite and TABLE 11 60 polyvalent metal salt to the polymer containing a phenol Parts overcame the decreased resistance to degradative deterio- Sample ration upon exposure to elevated temperatures resulting C D from the addition of the phenol. Moreover, no discolora- Polypropylene m; 1 100 0 tion was noted. The organic phosphorus acid and polygi f g g g g- 8 65 valent metal salt are thus valuable in combination with zriii; ih yl ii iroai ji" :III: 1 0 some stabilizers which, although valuable in preserving Melt Indem 2 7 2 8 some other physical property of a polymer, diminish its Migo' 1.1111111: III 3115 2511 high temperature stability. M6000 FJMi 11.7 92 Heat Ageing at 150 0., Hours to failure 14. 0 135. 5 Example 5 These data clearly indicate that the diphenyl phosphite A series of stabilized polypropylene compositions were and zinc 2-ethyl hexoate increased the resistance of the prepared, using various quantities and combinations of polymer to degradative deterioration on prolonged exstabilizers in accordance with the invention. A blend of posure to elevate temperatures. The melt index ratio was triphosphite and phenol was prepared before incorporalower for the polymer containing the diphenyl phosphite. tion with metal salt, the thiodipropionic acid ester, and

the resin, to prevent separation of the bisphenol. The con- TABLE VII centrates of phenol and triphosphite were blended with zinc 2-ethylhexoate and dilauryl thiodipropionate. Equal sample portions of the above described stabilizing mixtures were II II weighed and dispersed by hand stirring in powdered pre polypropylene u polymer) 100 100 viously unstabilized polypropylene (Sun Polymer). The g z gyg gggggi gg g gig 3%; so stabilibed p yp py was Compared Wlth S1H1 11ar1Y 4,4'-th1Qbis a rewar-5 5E513511515.165 0.10 0. '10 stabilized polypropylene to which diphenyl phosphite or hgfig lzfilg 3 dioctyl phosphite had been added, the polymer alone, and Melt Index, MW II" 117 the polymer stabilized with diphenyl or dioctyl phosphite 10 Agineat150 o o f eonly.

TABLE V Parts Sample No.

R s T i U v w X Y z AA. BB 00 DD Pol r0 ylene (Sun Polymer) .100 100 100 100 100 100 100 100 lsocllz yl iliphenyl phosphite. 0. 0. 14 0. 14 0. 28 0. 28 0. 28 0. 28 O. 14 Zinc 2-ethylhexoate 0. 06 0.06 0.06 0.06 0.06 0.12 0.12 0 12 0.12 0.06

"2.22 .3 1 er .0. 05 0.05 0.05 0.10 o. 10 0.10 0.0 0.05 Dilauryl thiodipropionate O. 0. 25 0. 5 0. 5 0. 5 0. 5 0. 25 Diphenyl phosphite 05 0. 10- 0 05 I 0.10- Dioctyl phosphite 0. l0 0. 10 M1 2.7 2.7 2.7 27 '29 3.1- M6000 1: 22. 4 43. 2 24. 0 20.0 .23. 0 2 3 A comparison of the melt indices obtained from these tests indicates, as above tabulated, that the organic phosphorous acid appreciably increased the thermal stability of the polypropylene, in conjunction with the other sta- I A series of compositions, using previously unstabilized polypropylene, and various quantities and combinations of stabilizers in accordance with the invention, and in the proportions indicated in the table below, were prepared in accordance with the method described in Example 5. The effect on the stabilization of the polymer by the addition of diphenyl phosphite was noted.

TABLE VI Parts Sample No. M

EE FF G G HH Polypropylene (Profax 6501)-.. 100 100 100 Isooctyl diphenyl phosphite.- 0.14 0. 14 0.28 0. 28 Zinc Z-ethylhexoate 0. 06 0.06 0. 12 0. l2 4,4-thiobis(2-tert-butyl-5-methylphenol) 0. 05 0. 05 0. 1O 0. 10 Dilauryl thiodipropionate 0.25 0.25 0. 50 O. 50 Diphenyl phosphite 0. 05 0. 05 Melt Index:

M 3. 1 3. 1 3. 1 500 F 11. 1 48. 6 25. 0 Heat Aging at 150 0., Hours to t' 500 420 765 In each of the above samples the greater heat stability, as evidenced by the lower melt index and improved heat aging, together with absence of discoloration, was achieved with diphenyl phosphite as a stabilizer.

Example 7 A series of polypropylene stabilizing combinations was prepared in accordance with Example 5 using the proportions of Table VII below. Diisooctyl phosphite was used as the organic phosphorous acid stabilizer. The portions of stabilizers were weighed and dispersed by hand stirring in powdered previously unstabilized polypropylene (Sun Polymer). This polymer as supplied had a melt index of 3.0, ASTM D1238-57T at 230 C. The mixture was placed on a 2-roll mill and fluxed for five minutes at 170i2 C. Pieces cut from the milled sheet were used in the tests.

Example 8 Polypropylene stabilized with triphenyl phosphite transesterified with 0.5 mole of 'n-butylidene-4,4'-bis (2-tertbutyl-S-methylphenol) and 2 moles of tridecyl alcohol, in combination with dilauryl thiodipropionate was compared with a polymer so stabilized containing zinc 2-ethylhexoate and'diphe'nyl phosphite as additional stabilizers.

The transesterified blend of phosphite, alcohol and phenol was prepared before incoporation' with the polypropylene. 4,4'-n-butylidene-bis (2-tertiary-butyl-5-methylphenol) (0.5 mole), triphenyl phosphite (one mole) and sodium hydroxide (0.5 'g.) were stirred and heated at to C. for three hours, and vacuum stripped to C. on the water pump. Next, the tridecyl alcohol (2 moles) was added and the mixture again'vacuum stripped to 170 C. on the water pump. At the end of this'time, a clear brown solution had formed, and this solution remained homogeneous at room temperature.

The stabilizers were weighed and dispersed by' hand stirring in powdered previously unstabilized polypropylene (Profax 6501) in the proportions indicated in the following table. The resulting mixtures were each placed on a 2-roll mill and fluxed for five minutes at 170i -2 C. Pieces cut from the milled sheet were tested as in the previous examples.

TABLE VIII The diphenyl phosphite and zinc 2-ethylhexoate appreciably reduced the degradative decomposition .of the polypropylene due to exposure to heat, as evidenced by lower melt index and absence of discoloration.

. Example 9 Commercially available p'restabilized polypropylenes,

1 7 Profax 6511 and 6512, were compared with such polymers to which strontium laurate and di(octylphenyl) phosphite had been added in accordance with this invention in the proportions indicated in the table below:

TABLE IX Parts Sample No.

MM NN PP Commercial Prestabilized Polypropylene (Profax 6511) 100 100 Commercial Prestabilized Polypropylene (Profax 6512) 100 100 Di(octylphenyl) 0.1 0. 1 Strontium laura 0. l 0. 1

A comparison of the final melt indices indicated that the addition of the di(octylphenyl) phosphite andstrontium laurate ,to commercially available prestabilized polypropylene markedly improved its thermal stability as evidenced by its lesser increase in melt index, and lack of discoloration upon prolonged exposure to elevated temperatures. A, v

Example 10 In order to show that the acid phosphites of the invention are not equivalent to neutral phosphites when used in conjunction with a polyvalent metal salt and a phenol, the followig tests were carried out.

18 Example 11 In addition, in order to show that the acid phosphites of the invention and the neutral phosphites are not equivalent to one another when used in conjuct'ion with the metal salt and the phenol, the nitrogen dioxide (N0 test which is in essence an accelerated ageing test was carried out. Five samples were prepared as described hereinbefore having the following compositions:

posed to nitrogen dioxide (N0 fumes for 15 min. to 24 hrs. and the color-of each sample was observed. Table XIII below sets out the data obtained in :this test. 0.090 part triisooctyl phosphite, 0.066 part triphenyl phosphite and 0.05 part diphenyl phosphite contain equivalent amounts of phosphorus.

TABLE XIII Time of Exposure U U W WW XX YY to N0: fumes 0 Colorless. Colorless Colorless Colorless Colorless. 15 mm Light brownish gray.-- Light brownish gray... Brownish gray... Brownish gray- Do. 2 hrs Yellowish Yellowish -do do Do. 24 hrs .-d .do Very light yellowish.

. Four polypropylene compositions named in Table X, labeled QQ, RR, SS, and T1", respectively, were prepared by weighing and dispersing by hand stirring the phosphite, phenol and metal salt named in Table X in powdered Monoisooctyl phosphite 0.069 part triisooctyl phosphite and 0.05 part diisooctyl phosphite contain-equivalent amounts of phosphorus.

The samples so prepared were in each case placed on a two-roll mill, fiuxed for five minutes at 170:2 C, and sheeted off. Pieces cut from the milled sheets were used in determining melt index using ASTM D -l238-57T at 230 C.

TABLE XI Melt Index Mao min. at m E... tuo i k/Mi The above data clearly indicate that the melt index ratio for each of Samples SS and TI which contain an organic phosphorous acid in accordance with the teaching of this invention, was substantially lower than that of Samples QQ and RR which contained a trialkyl phosphite, namely triisooctyl phosphite. In fact, the melt index ratio of Sample SS which contained diisooctyl phosphite was about 85% lower than that of Sample QQ, and about 55% lower than that of Sample RR and the melt index ratio of Sample SS which contained monoisooctyl phosphite was about 175% lower than that of Sample QQ and about 130% lower than that of Sample RR.

The above data clearly show that upon exposure to N0 fumes, Samples UU and VV, which contained a neutral phosphite, turned a light brownish gray after 15 min. of exposure to N0 fumes, and upon .2 hrs. and 24 hrs. exposure to N0 fumes exhibited a definite yellow coloration. Samples WW and XX exhibited a brownish gray color after 15 min. and 2 hrs. The color change in Samples UU to XX was of a significant intensity to render the samples less suitable for commercial use unless colored to a darker shade.

Sample YY, which contained as the phosphite an acid phosphite in accordance with the instant invention, remained colorless after 15 min. exposure to the N0 fumes, and after 2 hrs. and 24 hrs. exposure was observed to be substantially colorless, containing only a slight trace of yellow tint.

Example 12 TABLE XIV Sample No.

Polypropylene (Profax 6501) Di(nonylphenyl) phosphit Calcium oetoate Dilauryl thiodipropionate 1,1,3-tris(2-methy1-4-hydroxy-5-tert-butylphenyl) butane. Melt Index:

M10 min. 550 F Heat Ageing at 0., Hours to failure The above data clearly indicate that the four component stabilizer combinations of the invention markedly 19 improves the resistance of polypropylene to degradative deterioration on prolonged exposure to elevated temperatures.

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A stabilizer combination for use in improving the resistance of olefin polymers to deterioration in physical properties on exposure to heat, consisting essentially of from about 0.1 to about 25 parts by weight of an organic phosphorus acid containing trivalent phosphorus, and from about 2.5 to about 75 parts by weight of a Group II metal salt of a non-nitrogenous monocarboxylic acid having from about six to about twenty-four carbon atoms, the stabilizers being compatible with polypropylene and having a low vapor pressure at polypropylene working temperatures.

2. A stabilizer combination in accordance with claim 1 comprising in addition another olefin polymer stabilizer.

3. A stabilizer combination in accordance with claim 2 in which the other stabilizer is from about 2.5 to about 50 parts by weight of a phenol.

4. A stabilizer combination in accordance with claim 2 in which the other stabilizer is from about 2.5 to about 50 parts by weight of a bicyclic phenol.

5. A stabilizer combination in accordance with claim 2 in which the other stabilizer is from about 1 to about 50 parts by weight of a triphosphite.

6. A stabilizer combination in accordance with claim 2 in which the other stabilizer is from about 5 to about 100 parts by weight of a thiodipropionate.

7. A stabilizer combination in accordance with claim 1 consisting essentially of from about 0.1 to about 25 parts by weight of an organic phosphorus acid containing trivalent phosphorus, from about 2.5 to about 75 parts by weight of a Group II metal salt of a non-nitrogenous monocarboxylic acid having from about six to about twenty-four carbon atoms, from about 2.5 to about 50 parts by Weight of a phenol, and from about 5 to about 100 parts by weight of a thiodipropionate.

8. A stabilizer combination in accordance with claim 1 consisting essentially of from about 0.1 to about 25 parts by weight of an organic phosphorus acid containing trivalent phosphorus, from about 2.5 to about 75 parts by weight of a Group H metal salt of a non-nitrogenous monocarboxylic acid having from about six to about twenty-four carbon atoms, from about 2.5 to about 50 parts by weight of a phenol, from about 1 to about 50 parts by weight of a triphosphite, and from about 5 t about 100 parts by weight of a thiodipropionate.

9.- A stabilizer combination in accordance with claim 1 consisting essentially of from about 0.1 to about 25 parts by weight of an organic phosphorus acid containing trivalent phosphorus, from about 2.5 to about 75 parts by weight of a Group II metal salt of a non-nitrogenous monocarboxylic acid having from about six to about twenty-four carbon atoms, from about 2.5 to about 50 parts by weight of a bis-phenol, from about 1 to about 50 parts by weight of a triphosphite, and from about 5 to about 100 parts by weight of a thiodipropionate.

10. An olefin polymer composition having improved resistance to deterioration upon exposure to heat com prising an olefin polymer prepared from olefin monomers 2(} I 9 containing from two to six carbon atoms and from about 0.005 to about 2.5% by weight of a stabilizer combination in accordance with claim 1. w

11. An olefin polymer composition in accordance with claim 10, in which the olefin polymer isa propylene polymer.

12. An olefin polymer composition in accordance with claim 11, in which the propylene polymer is polypropylene.

13. An olefin polymer composition having improved resistance to deterioration upon exposure to heat, comprising an olefin polymer prepared from olefin monomers containing from two to six carbon atoms, and from about 0.005 to about 2.5% by weight of a stabilizer combination in accordance with claim 6.

14. An olefin polymer composition having improved resistance to deterioration upon exposure to heat, comprising an olefin polymer prepared from olefin monomers containing from two to six carbon atoms, and from about 0.005 to about 2.5% by weight of a stabilizer combination in accordance with claim 7.

15. An olefin polymer composition having improved resistance to deterioration upon exposure to heat, comprising an olefin polymer prepared from olefin monomers containing from two to six carbon atoms, and from about 0.005 to about 2.5% by weight of a stabilizer combination in accordance with claim 8.

16. A stabilizer combination for use in improving the resistance of olefin polymers to deterioration in physical properties on exposure to heat, consisting essentially of from about 0.1 to about 25 parts by weight of an organic phosphorus acid containing trivalent phosphorus, from about 2.5 to about parts by weight of a Group II metal salt of a non-nitrogenous monocarboxylic acid having from about six to about twenty-four carbon atoms, and from about 2.5 to about 50 parts by weight of a phenol.

17. A stabilizer combination in accordance with claim 16 including in addition from about 1 to about 50 parts by weight of a triphosphite.

18. A stabilizer combination in accordance with claim 16 including in addition from about 5 to about parts by weight of a thiodipropionic acid ester.

References Cited UNITED STATES PATENTS 2,860,115 11/1958 Hecker et al. 3,033,814 5/1962 Tholstrup 260-45.85 3,069,369 12/1962 Galbraith et al. 3,103,501 9/1963 Shearer et al. 26045.7 3,115,465 12/1963 Orlofi. et a1 26045.95 3,119,783 1/1964 Baum 26045.95 3,167,526 1/1965 Nicholson. 2,462,331 2/1949 Myers 26O23 3,297,631 1/1967 Bown et al. 260-45.95

FOREIGN PATENTS 1,235,047 5/1960 France.

577,252 7/1959 Belgium.

DONALD E. CZAJA, Primary Examiner. R. A. WHITE, Assistant Examiner.

UNI'IECD SiA'iiilS PATE'INT OFFICE CERTIFICATE OF CORRECTIQN Patent No. 3,406,135 Dated October 15, 1968 Inventor(s) Arthur C. Hecker and Norman L. Perry- [t is certified that: error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 70,"addition" should be --additional. Column 4, line 26, "prepared" should be --preferred--; line 43, benzenephophonous" ShOllll be --benzenephosphonous--. Column 6, line 4 "and" should be --any--. Column 7, line 51, first formula should be CH third formula should be l CH,

--CH- last formula should be deleted (-CH -SCH Column 8,de1ete line 19, and insert on ageing imparted by the triphosphite in relatively high Column 9, line 67, "proyl" should be propyl Column 13, line 58, "fixe" should be --five--; line 74, "elevate" should be --elevated--. Column 15, line 7, "stabilibed" should be --stabilized--. Column 16, Table V, under 4th entry for CC, "0. 0" should be -0. l0--. Column 17, line 49, Table X, under last entry for TT, 0,05" should be -*-0.05--. Column 18, lineS "conjuction" should be --conjunction--.

In the original Letters Patent, columns 9 to 12 erroneously follow columns 3 and 4, and should, of course, follow olumuns 7 and 8 insteat SIGNED AND SEMEU MAY 1 21971! .Attcst:

Edward M. FlcrrL-er, Ir.

Ancfiting Officer WILLIAM In. SLIEHUYLER, J'R.

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